Document share page view

Example:
https://apps.npr.org/liveblogs/20170821-eclipse/share.html

In quick testing with the elections liveblog url, the twitter campaign URLs weren't getting appended to the URLs. But it's still a nice view of all the stories in the liveblog.

Also: How does this work (or not) with the separate share pages that were added w/ elections 2018 development?